DESCRIPTION: (Adapted from the investigator's specific aims) This is a pilot, longitudinal study, employing thermal ionization/mass spectrometry (TI/MS) isotopic dilution analysis in an ultraclean laboratory, of environmental sources of childhood blood lead. The study will be conducted on 24 children 18-36 months old who live in the urban residential area of a smelter city where the air lead is now negligible, but no soil lead remediation programs have been undertaken. It tests the hypothesis that food lead, non-food lead and endogenously mobilized lead can be quantified as the primary sources of childhood blood lead. In this study "food" or PbF means the 24 hour intake of all food and water after household preparation but before it is handled by the child. The isotopic ratios of lead in the adult diet are remarkably constant. If this is true in children, then random variances in the isotopic ratios of blood lead (PbB-IR) reflect individual differences in non-food sources. In this study hand dust lead (PbH) serves as the surrogate for composite non-food sources in the environment. It is proposed that cyclic changes in the concentrations or isotopic ratios of blood lead, independent of the contributions of food, air and hand dust lead, represent mobilization of endogenous sources of blood lead.